Conventionally, in order to provide a high-speed response to an access request, an in-memory database (hereinafter called an “in-memory DB”) affords data residency in a volatile memory, for example, so that time-consuming I/Os to and from an external storage apparatus are not performed or are limited.
By the way, in a database management system, because data disappears from a memory when a system stops, the in-memory DB backs up data to an on-disk database (hereinafter called “on-disk DB”) which holds data in an external storage apparatus.
In order to back up data to the on-disk DB, data replication technology which matches the data of the in-memory DB with that of the on-disk DB is required.
In a technology of the data replication, Non-PTL4 discloses a technology which uniquely identifies a record which corresponds to each of the records in the data of the database from data of another database by using an unique index which are defined in tables of two databases to be replicated.
The unique index used in the above data replication technology may not exist in an user database design. In this case, there are problems such as an increase in a labor of the user adding the unique index to the database, an increase in the usage amount of the external storage apparatus due to storing the unique index, and an increase in processing overhead due to updating the unique index.
Against these problems PTL1 discloses a technology which obviates the need to define an unique index by creating a mapping table for physical storage location information between different databases.
Furthermore, when a record is added to the data replication source, not only the data replication source is accessed but also the data replication destination is accessed, physical storage location information, which the data replication destination acquires determined, so that the data replication of the record is completed.
As described in Non-PTL2 and 3 (Non-PTL3 is a translation of Non-PTL2 in Japanese), this is because unused area information is referenced to determine the physical storage location information which is the record addition destination in order to hold information of the unused area in the database.